Is it normal i feel weak when talking about blood?

Whenever someone talks about blood I get this tingly feeling and I feel weak. When someone's talking about blood, I try to clench my fists but I can't. I can close my fist but I can't like clench it really hard. If I were to clench really hard then I can feel my nails pressing my palms, but not when someone's talking about blood. I also can't grip a pencil super tightly. I can just loosely hold it. This also happens SOMETIMES when I see blood, not all the time. I also get this tingly and weak feeling in my shoulders and knees. This has been going on for as long as I can remember, but I never paid attention to it, until today. In science we were learning and watching a video about blood, I had to take notes. I ignored the feeling in my knees and shoulders. When I tried to grip my pencil, I couldn't grip it tightly. It wasn't falling out of my hand or anything, I just couldn't hold it tight. Then I tried my hands I can close my hands but not clench them tightly. I finally acknowledged my weak shoulders and knees. I had ignored this weak feeling for years, but I always knew it was happening, I just ignored it. But now, I feel like this is unusual. Is this normal?